Epitaxial growth technique



Dec. 29, 1-970 PANlSH ETIAL 3,551,219

EPITAXIAL GROWTH TECHNIQUE Filed May 9, 1968 FIG. 3A FIG. 3B

M. B. PAN/SH lNVENTO/PS SUMSK/ United States Patent 3,551,219 EPITAXIALGROWTH TECHNIQUE Morton B. Panish, Springfield, and Stanley Sumski, New

Providence, N.J., assignors to Bell Telephone Laboratories,Incorporated, Murray Hill and Berkeley Heights,

N.J., a corporation of New York Filed May 9, 1968, Ser. No. 727,927 Int.Cl. H01l 7/34 US. Cl. 148171 7 Claims ABSTRACT OF THE DISCLOSUREEpitaxial films of Group III(a)-V(a) compounds are grown by tippingtechniques utilizing a novel apparatus capable of removing deleteriousoxides from the surface of source solutions prior to the depositionthereon of seed crystals. The described technique permits the growth ofelectroluminescent p-n junction devices capable of emitting light atroom temperature in the visible portion of the spectrum.

This invention relates to a technique for the growth of epitaxial filmsof Group III(a)-V(a) compounds of the Periodic Table of the Elements.More particularly, the present invention relates to a solution epitaxytechnique for the growth of Group III(a)-V(a) compounds.

Recently, there has been a birth of interest in mixed crystals ofgallium aluminum arsenide and gallium aluminum phosphide, it having beentheorized that such crystals are capable of emitting light in thevisible portion of the spectrum. Heretofore, workers in the art havesucceeded in growing epitaxial films of gallium aluminum arsenide bydipping techniques. However, attempts to grow gallium aluminum phosphidein this manner have not proven fruitful. A later stage in thedevelopment of the art involved attempts by workers in the art to growepitaxial films of gallium aluminum arsenide, and gallium aluminumphosphide by conventional tipping techniques. Unfortunately, thepresence of a deleterious oxide scum on the surface of source solutionsprevented uniform wetting and growth of the seed crystal, therebyprecluding the use of this procedure.

In accordance with the present invention, a tipping technique isdescribed for the growth of epitaxial films of Group III(a)-V(tr)compounds utilizing a novel apparatus. The described technique resultsin the growth of epitaxial gallium aluminum arsenide, gallium aluminumphosphide, aluminum arsenide, and aluminum phosphide. Briefly, theinventive procedure involves growth by solution epitaxy in a tippingapparatus including amoveable substrate holder adapted with means forremoving deleterious'oxide contaminants from the surface of a sourcesolution prior to growth. Operation of the technique in the describedmanner permits the growth of the noted epitaxial films as well as thegrowth of a pm electroluminescent junctions capable of emitting redlight at room temperature.

It will be understood by those skilled in the art that for the purposesof the present invention the Group III(a)-V(a) compounds of the PeriodicTable of the Elements are those set forth in the Mendelyeev PeriodicTable appearing on page B2 in the 45th Edition of the Handbook ofChemistry and Physics, published by the Chemical Rubber Company.

The invention will be more readily understood by reference to thefollowing detailed description taken in conjunction with theaccompanying drawing wherein:

FIG. 1 is a front elevational view of an apparatus employed in thepractice of the invention;

3,551,219 Patented Dec. 29, 1970 FIG. 2 is a cross-sectional view of thecrystal growth tube of FIG. 1; and

FIGS. 3A through 3D are cross-sectional views in successive stages ofmanufacture of a p-n junction device of the present invention.

With further reference now to FIG. 1, there is shown a typical crystalgrowth apparatus utilized in the practice of the present invention.Shown in the figure is a crystal growth tube 11 typically comprised ofquartz having an inlet 12 and an outlet 13 for the introduction andremoval of gases, respectively, and a boat assembly 14. Boat 14 hasdisposed therein a moveable substrate holder 15, a pair of wells 16 and17 for containing source solutions, and means 18 for actuating holder15. Holder 15 is also'adapted with means 19 and 20 for removing surfaceoxides and associated contaminants from the surface of source solutionscontained in wells 16 and 17. Tube 11 is shown inserted in furnace 21,adapted with a viewing port 22, furnace 21 being positioned upon cradle23, which permits tipping of the growth tube 11.

FIG. 2 is an enlarged view :partly in section of tube 11, substrateholder 15 having contained therein a substrate number 24.

Referring now to an exemplary technique employed herein, a suitablesubstrate material is obtained, typically from commercial sources. Thus,for example, the substrate may be gallium arsenide or gallium phosphide.The material so obtained is next lapped and cleaned in accordance withconventional techniques to yield smooth surfaces. A cross-sectional viewof a typical substrate is shown in FIG. 3A (n-type for exemplarypurposes).

Next, an apparatus similar to that shown in FIG. 1 including a quartzgrowth tube and a carbon boat is selected. Following, a source solutionconsisting of either gallium, aluminum and arsenic, or gallium, aluminumand phosphorous is prepared. This end is attained by adding knownquantities of solid gallium arsenide or gallium phosphide (99.9999%purity) obtained from commercial sources to known amounts of aluminum(99.9999% purity) contained in a solution of gallium so as to result insolutions of the desired composition. For the purposes of the presentinvention, the amount of aluminum employed ranges from approximately02-15 atomic percent in the gallium-aluminum-arsenic solutions, andapproximately 0.2-4 atomic percent in galliumaluminum-phosphorussolutions, the lower limits being dictated by considerations of theternary phase diagram. The use of less than the noted amounts ofaluminum is difficult because of the properties of thegallium-aluminum-arsenide phase system, whereas the use of greater thanthe noted amounts results in either aluminum arsenide or aluminumphosphide. An appropriate dopant may be added in order to obtain anepitaxial film of desired conductivity type. The components for thesolution or solutions are placed together in the wells of the apparatuswhich are designed so that the upper surface of the solution is slightlyabove the edge of the well, the components being mixed and dissolvedduring subsequent heating. Then, the substrate member is inserted in thesubstrate holder and the system flushed with nitrogen. After flushingthe system, pre-purified hydrogen is admitted thereto, and thetemperature elevated to either 1050 C. for gallium arsenide, or 1150 C.for gallium phosphide, the temperature maximum being dictated byconsiderations relating to substrate damage and concomitant loss ofarsenic or phosphorus. Following, the ram of the apparatus is activatedby tipping the boat, thereby causing the leading edge of the substrateholder to remove the oxide scum from the surface of the solutioncontained in one of the wells and causing deposition of the substrateupon a clean oxide free solution. A controlled cooling program is theninitiated at a rate sufiicient to grow an epitaxial film of the desiredthickness. The film 32, so grown, for example, of n-type conductivitymay be seen by reference to FIG. 3B. At this point in the processing, areverse tip may be effected so as to cause the substrate holder to shiftin the opposite direction and deposit the substrate member on a cleanoxide surface of a solution of differing concentration or containing adifferent dopant, thereby forming an epitaxial film 33 of, for example,p-type conductivity (FIG. 3C). In this manner, it is possible to form ap-n junction structure of the type noted above.

An example of the present invention is set forth below.

EXAMPLE This example describes the fabrication of an electroluminescentp-n junction device utilizing gallium aluminum arsenide grown inaccordance with the invention.

A gallium arsenide wafer having faces perpendicular to the llldirection, obtained from commercial sources, was selected as thesubstrate member. The wafer was lapped with 305 Carborundum, rinsed withdeionized water, and etched for 30 seconds in a chlorine-methanolsolution to remove surface damage. Following, a galliumaluminum-arsenicsolution containing 0.8 atom percent aluminum, 9.2 percent arsenic, and90 percent gallium, was prepared by adding 150 milligrams of galliumarsenide (99.9999% purity) obtained from commercial sources, and 50milligrams of gallium arsenide doped to 10 atom/cm. with tellurium to 1gram of liquid gallium metal (99.9999% purity) containing 4 milligramsaluminum. The aluminum was prepared by cutting 4 milligrams of aluminumfrom a rod, etching it in sodium hydroxide and rinsing in deionizedWater. The tellurium in the tellurium doped gallium arsenide added tothe solution was the source of tellurium to make the grown layer n-type.The components of the mixture were then placed in a well of theapparatus shown in FIG. 1. A second solution prepared in the mannerdescribed above was placed in the other well of the apparatus. However,this solution contained 5 milligrams of zinc, and instead of telluriumdoped gallium arsenide all of the gallium arsenide used for the solutionwas undoped. The substrate member was then inserted in the substrateholder of the apparatus. The system was then sealed and nitrogenadmitted thereto for the purpose of flushing out entrapped gases. Next,hydrogen was passed through the system and the temperature thereofelevated to approximately 1040 C. After attaining this temperature, theoven was cooled to 1000 C. and the ram in the apparatus was actuated bytipping the boat, thereby resulting in removal of the oxide scum fromthe surface of the solution containing the tellurium dopant, and thesubstrate member deposited thereon. At this point, a controlled coolingprogram at 2.5 C. per minute was initiated and the source solutioncooled to approximately 990 C. over a time period of 4 minutes, therebyresulting in the formation of an epitaxial film of n-type galliumaluminum arsenide upon the gallium-arsenide substrate, such film havinga thickness of approximately 0.87 mil. Then the apparatus was tipped inthe other direction and the gallium arsenide substrate bearing an n-typelayer of gallium aluminum arsenide was again moved by actuating the ramof the apparatus and positioned upon the surface of the solutioncontained in the other well. The controlled cooling program wascontinued and a film of p-type gallium aluminum arsenide was grown uponthe previously grown n-type gallium aluminum arsenide film over atemperature range of 990970 C. during a time period of 8 minutes. Afterattaining the desired p-n junction structure, the apparatus was tippedback to the horizontal and cooled to room temperature.

The resultant p-n structure was then diced to a geometry designed fordevice applications. Next, the bottom surface of the substrate wascoated with 5000 A. Of ti anium and 5000 A. of gold by conventionalevaporation techniques. Contact to the n-type material was made bydepositing approximately 1x10 A. of tin thereon. The resultant structureis then mounted on a conventional transistor type header 34 (FIG. 3D)using low melting solder. The resultant structure may be seen in FIG. 3Din cross section. Ohmic contact is made to the p-side by means of tinfilm 35 and gold wire 36 and to the n-side by means of the titanium-goldfilm 37.

In order to demonstrate the efficacy of the resultant devices, the leadswere connected to a D-C source under forward bias conditions, the pluslead to the p-region and the minus lead to the n-region. At roomtemperature, at a forward voltage of +10 volts, the device was found tocarry about 10 milliamperes of current accompanied by the emission ofred light. The measured external quantum efficiency as determined bymeans of a calibrated solar cell was found to be approximately 1 l0percent.

While the invention has been described in detail in the foregoingspecification and the drawings similarly illustrate the same, theaforesaid is by way of illustration only and is not restrictive incharacter. The modifications which will readily suggest themselves topersons skilled in the art are all considered within the scope of thisinvention, reference being had to the appended claims. It will also beunderstood that the invention may be employed in the growth of epitaxialfilms which do not include aluminum.

What is claimed is:

1. A method for the growth of epitaxial films of Group III(a)-V(a)compounds of the Periodic Table of the Elements comprising the steps of(a) inserting a substrate wafer in a crystal growth apparatus includinga moveable substrate holder having means for removing contaminants fromthe surface of a source solution, (b) placing at least one sourcesolution in said apparatus, (0) heating said source solution to atemperature within the range of l0501150 C., (d) tipping said substrateholder thereby removing contaminants from the surface of said sourcesolution and depositing said substrate thereon, and (e) initiating acontrolled cooling program which results in the growth of an epitaxialfilm upon said substrate.

2. Method in accordance with claim 1 wherein said layer is galliumaluminum arsenide.

3'. Method in accordance with claim 1 wherein said layer is galliumaluminum phosphide.

4. Method in accordance with claim 2 wherein said source solutioncomprises from 0.215 atomic percent aluminum.

5. Method in accordance with claim 2 wherein said source solutionincludes tellurium.

6. Method in accordance with claim 2 wherein two source solutions areemployed and said substrate holder is tipped in the opposite directionafter the growth of a first epitaxial layer.

7. Method in accordance with claim 3' wherein said source solutioncomprises from 0.2-4 atomic percent aluminum.

References Cited UNITED STATES PATENTS 2,962,363 11/1960 Martin 148-1.62,977,258 3/1961 Dunkle 148-16 3,158,512 11/1964 Nelson et al l481.53,463,680 8/1969 Melngailis et a1. 148-172 L. DEWAYNE RUTLEDGE, PrimaryExaminer E. L. WEISE, Assistant Examiner US. Cl. X.R.v

